FRIDAY, July 19 (HealthDay News) -- A treatment in which progressively larger servings of milk are given to children with milk allergies provides long-term protection for some youngsters, but others lose their tolerance over time, a new study says.

The investigators also found that many children continued to have intermittent symptoms and some had severe allergic reactions even after showing improvement in the early stages of treatment.

Previous research on this form of so-called "oral immunotherapy" showed promise. But the first long-term study of the treatment showed the need for more studies with longer follow-up, said the researchers from the Johns Hopkins Children's Center, in Baltimore.

"While many children were clearly better off with treatment, our results raise troubling questions about the long-term risk for future reactions among children treated with this approach," lead investigator and pediatric allergist Dr. Corinne Keet said in a center news release.

Senior investigator Dr. Robert Wood, director of the center's division of pediatric allergy and immunology, added: "Our results are a clear 'proceed with caution' sign. While we've been excited about this treatment, we also knew there were many questions that had to be answered. Our findings provide some of those critical answers."

The study included 32 children with milk allergies who were followed for three to five years after they completed the therapy. By the end of the original treatment, all but three of the children showed some improvement and were able to consume at least some milk.

Eight children remained symptom-free over the long term, 12 had frequent allergy symptoms when they drank milk and seven eventually stopped consuming milk or were limited to very small amounts. Six children suffered serious allergic reactions, the study authors said.

The study was published online recently in the Journal of Allergy and Clinical Immunology.